1. Field of the Invention
This invention relates to a tube-pump feeding fluid enclosed in a ring-shaped elastic tube disposed along the inner wall of a cylindrical chamber by a rotating press means disposed within said elastic tube.
2. Description of the Prior Arts
Two types of the tube-pump one of which presses an elastic tube directly by means of a rotating press means such as a rotating roller, and another where said rotating press means consists of a ring-shaped pressure member disposed within an elastic tube and an eccentric cam device driving said ring-shaped pressure member, indirectly pressing said elastic tube by driving said pressure member in a circular motion along the inner wall of a cylindrical chamber have been known. For instance, Laid-Open Patent Hei 5-133350 shows a tube-pump of the latter type in FIG. 3 wherein an elastic tube is indirectly pressed. This tube-pump of indirect pressing type is advantageous over the direct pressing type in terms of the less damage and longer life of elastic tube.
However, when said ring-shaped pressure member is driven by rotating said eccentric cam device, said pressure member is rotated in a direction opposing to the rotation of said eccentric cam device applying a continuous pulling force to said elastic tube in a rotating direction of said pressure member. Although said pulling force is negligibly small in comparing to the force directly applied on said elastic tube by a roller, said elastic tube would be gradually elongated into the rotating direction of said pressure member when said pump is continuously operated. Thus, a number of troubles including a change of inner diameter of said elastic tube changing the output capacity of pump, a change of load of motor driving said eccentric cam device, a possible damage of elastic tube by the elongation of said tube, etc; are produced.